Typical examples of communication systems comprising data generating sources arranged in a straight line or a loop, these data generating sources being connected via transmission paths to data processing centers that centrally control these devices are railroad management systems, road management systems, sewer management systems, airport management systems, river management systems and subway management systems.
In a railroad management system, a control center exists within an administrative territory, monitoring cameras and train detection sensors are positioned along the railway within the administrative territory, and information from these cameras and sensors is collected at the control center. Signal devices and other means of communicating control information to trains are also positioned along the railway. Accident information from adjacent administrative territories is also collected at the control center, where various judgements are made using this information and the information from the administrative territory in question, and then based on the results of these judgements, the operation of the trains is controlled and other railway management procedures are implemented using signal devices and such.
As can be gleaned from this example of a railroad management system, with this type of communication system, information has been collected via communication lines connecting data generating sources to the control center on a one-to-one basis, and control of signal device displays has been implemented via communication lines running from the control center on a one-to-one basis. However, developments aimed at making asynchronous transfer mode (ATM) switching systems more practical have made rapid progress recently, and by applying this ATM technology to communication systems such as the one described above, it has become possible to construct flexible systems that make the most of the advantages offered by ATM.
FIG. 13 outlines the system configuration achieved by applying ATM technology to the various management systems described above, and more particularly, what happens when a fault occurs. This system is configured with a plurality of distributed switching components (92), which are connected to a center switching component (91) via transmission lines (93). If a fault (95) similar to the one indicated by the X in the figure were to occur in this system today, switching components (92-2 and 92-3) adjacent to the fault point (95) would each execute loopback, thereby making it possible for the system to autonomously recover communication functions via the route indicated in the figure by the dotted line.
Thus, it is possible for a system with the above-cited configuration to use loopback to maintain communications when a fault occurs, but when this communication system was applied to an actual railroad management system, the below-described problems arose. A railroad management system could be configured as shown in FIG. (14), comprising switching components (92-1-92-5) distributed along both sides of the railway (rail 100), a control center-based center switching component (91) that controls each of the switching components (92-1-92-5), this center switching component (91) being connected to each of the switching components (92-1.about.92-5) via loop-shaped transmission paths (93). Each of the switching components (92-1-92-5) is then equipped with input/output ports (94), with local communication terminals equivalent to the above-described monitoring cameras, train detection sensors and/or signal devices being supported via these input/output ports (94).
However, with this configuration, when an earthquake or some other disaster strikes and severs the railway, faults do not occur only in one place as indicated by the fault (95) shown in FIG. 13, but generally involve faults wherein the above-described loop is simultaneously cut in two locations opposite one another as with the fault (101) indicated in FIG. (14). When a situation of this sort occurs, switching components (92-1, 92-2 and 92-3) connected to the center switching component (91) via transmission paths (93) are capable of autonomously recovering communication functions by implementing the loopback described above, but switching components (92-4 and 92-5) on the other side, which are completely cut off by the breaks in the transmission paths (93), are unable to recover communication functions.
Instead of positioning switching components (92) in a loop along both incoming and outgoing railway lines (100), one possible method for configuring a system that overcomes this problem would be to construct loop-shaped networks for each railway line so that earthquake-caused faults would be limited to a single location. However, when loop-shaped networks have been constructed along railways, in some areas these loops have extended for several hundred kilometers, and have limited the response capabilities of conventional systems with only a single center switching component (91), resulting in a network that did not really possess the flexibility needed by a railroad management system.
Thus, with the conventional system described above, communication functions could be recovered autonomously by looping back to the center switching component from the switching components adjacent to the point where a fault occurred, but the fact that the basic configuration called for a plurality of distributed switching components to be controlled by a single center switching component was a problem in that the pattern of the generated fault often resulted in one of the loopback transmission paths to the center switching component being lost as described above, dealing a fatal blow to the autonomous recovery of communication functions.
Further, concerning the loss of the loopback transmission paths leading to the center switching component, this can be dealt with to a certain degree by redesigning the layout of the switching components, such as constructing a loop-shaped railway network, but the current practice of having only one center switching component limits the capabilities of a loop-shaped network that extends for several hundred kilometers, and this is a problem for railroad and other management systems in that the network lacks the flexibility to deal with changes.
An object of the present invention is to provide a communication system that is capable of doing away with the above-described problems, ensuring autonomous recovery of communication functions when faults occur, and enabling the construction of a highly flexible network with regard to various management and control requirements.